Pulmonary nodule

Nodules are the raw material of lung cancer screening and its main source of harm. A nodule is described by size, by density (solid, part-solid or pure ground-glass) and by growth. Solid nodules below a few millimetres are almost never cancer and are left alone or rescanned at long intervals; larger solid nodules and growing ones are worked up. Sub-solid nodules behave differently: a pure ground-glass nodule that persists may be adenocarcinoma in situ or minimally invasive adenocarcinoma, which grow very slowly and are followed for years, while the appearance of a solid component within one signals invasion. Spiculated margins, upper-lobe location and an emphysematous lung raise the probability of malignancy. Screening protocols differ in how they measure: the American trials used the largest diameter, NELSON used automated volume and volume doubling time, and the referral rate differed accordingly, 24.2 percent of NELSON-era American screens positive against 2.1 percent of NELSON participants referred for a suspicious nodule. Incidental nodules on scans done for other reasons are common and follow the same logic. In the National Lung Screening Trial, 96.4 percent of positive low-dose CT screens were false positives, and false positives led to 17 invasive procedures per 1,000 people screened.